identify carriers of the condition (people who don't have MD but have the potential to pass it on to their children)

determine a prenatal diagnosis (when a foetus is tested during pregnancy)

Genetic testing is likely to be used more often in the future, because knowing the precise cause of MD may determine what type of treatment will be most effective.

Identifying carriers

Some types of MD can be carried without causing clear signs of the condition. This applies to recessive inherited disorders, sex-linked conditions and even some dominant conditions. Genetic testing can determine who's carrying the disorder.

For example, a woman with a family history of Duchenne MD but no symptoms herself may be carrying the gene that causes it. DNA can be taken from cells in her blood, saliva or tissue and compared with a sample from a family member who has the condition, to find out if she's carrying the faulty gene.

If you or your partner are a carrier of MD and are at risk of passing the condition on to your child, your genetic counsellor will discuss your options with you.

Read more about the causes of MD for more information about how MD is inherited.

Prenatal diagnosis

Genetic testing can also be used for prenatal diagnosis. This is when a baby is diagnosed with MD before birth using tests carried out during pregnancy. You may be offered these tests if you're pregnant and there's a possibility that your unborn baby has MD.

There are two main ways of performing a prenatal diagnosis. One is chorionic villus sampling (CVS), which involves removing tissue from the placenta for analysis, usually after 11 weeks into the pregnancy.

The other method is amniocentesis, which isn't usually carried out until 15 to 16 weeks of pregnancy. A needle is inserted into your abdomen (tummy) so that a sample of the amniotic fluid that surrounds the foetus in the womb can be taken. Amniotic fluid contains cells that have been shed by the foetus.

Both CVS and amniocentesis carry a small risk of causing a miscarriage.

The cells from the foetus can be tested to determine whether they have the genetic mutation responsible for MD. If they do, the baby is likely to develop MD at some stage after birth.

If this is the case, your genetic counsellor can discuss your options with you, which will often include terminating the pregnancy. Such decisions can be very difficult and personal.

Be aware that there are limitations to this kind of diagnosis. Tests can give misleading or unexpected results. It's important to discuss prenatal testing and what the possible results mean before going ahead with the procedure. Expert genetic counselling can be very helpful in these circumstances to help people make the decision that's right for them.

A normal test result doesn't guarantee that the baby will be healthy. The test only looks for the particular type of MD in the family but not for all other possible problems. A prenatal diagnosis can only be carried out if there's a precise genetic diagnosis of the family's condition.

Newer tests are being developed that can be performed by taking a sample of blood from the mother and testing the free foetal DNA (ffDNA). This is known as non-invasive prenatal diagnosis (NIPD).

NIPD is currently used to determine the sex of a foetus when it's medically important to know this, as well as its Rhesus blood group. It's hoped that NIPD will soon be able to diagnose conditions such as Duchenne MD.

Pre-implantation genetic diagnosis (PGD)

For couples at risk of having a child affected by MD, another possible option is to use in vitro fertilisation (IVF) and then test early embryos for the condition. It allows only unaffected embryos to be transferred into the woman. This is known as pre-implantation genetic diagnosis (PGD).

While PGD has the advantage of avoiding the termination of foetuses affected by the condition, it also has a number of drawbacks. These include the modest success rate of becoming pregnant after IVF, as well as the substantial social, financial and emotional burdens of the combined IVF and PGD process. Apart from couples who need IVF so they can conceive a child, the number of people who use PGD is small.